Racket

ABSTRACT

A grommet of a racket includes a tubular part. The tubular part includes a through hole through which a string is passed. The through hole includes a base opening, a side wall, and a non-circular tip opening. Assuming an imaginary dividing plane that is perpendicular to a face of the racket and that divides the non-circular tip opening into a first opening portion and a second opening portion shorter than the first opening portion in a direction parallel to the face, an inside dimension of the first opening portion in the direction perpendicular to the face increases gradually from one end of the non-circular tip opening in the direction parallel to the face to the dividing plane. In the tubular part, the string passes through the first opening portion and is in contact with the side wall from the base opening to the tip opening.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Japanese Patent Application No. 2021-182156, filed on Nov. 8, 2021, the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present disclosure relates to a racket for use in tennis or the like.

2. Description of the Related Art

A tennis racket includes a frame and strings. In the tennis racket, the strings are typically passed through holes via a grommet. A proposal relating to the shape of the grommet is disclosed in Japanese Laid-Open Patent Application Publication No. 2015-217192.

SUMMARY OF THE INVENTION

A tennis player tries to hit the ball at the center of the face of the racket. However, in tennis playing, the ball is often hit at a point away from the center of the face. When the ball is hit at a point below the center of the face (point toward the ground), the ball flies at a small launch angle due to a change in the angle of the face. The small launch angle leads to a low trajectory of the ball. The ball flying in a low trajectory is likely to fail to pass over the net.

The present applicant aims to provide a racket capable of producing a stable trajectory of a ball even in the event that the ball is hit at a point away from the center of the face of the racket.

A racket according to the present disclosure includes:

(1) a frame;

(2) a grommet mounted on the frame, the grommet including a plurality of tubular parts; and

(3) strings forming a face of the racket.

Each of the tubular parts includes a through hole through which a corresponding one of the strings is passed. The through hole includes a base opening, a side wall, and a tip opening. At least one of the plurality of tubular parts includes a non-circular tip opening. Assuming an imaginary dividing plane that is perpendicular to the face and that divides the non-circular tip opening into a first opening portion and a second opening portion shorter than the first opening portion in a direction parallel to the face, an inside dimension of the first opening portion in a direction perpendicular to the face increases gradually from one end of the non-circular tip opening in the direction parallel to the face to the dividing plane. In the tubular part including the non-circular tip opening, the string passes through the first opening portion and is in contact with the side wall from the base opening to the tip opening.

With the use of the racket according to the present disclosure, a stable trajectory can be achieved even in the event that the ball is hit at a point away from the center of the face.

The above and further objects, features and advantages of the present disclosure will be more apparent from the following detailed description of preferred embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view showing a racket according to a first embodiment of the present disclosure.

FIG. 2 is an enlarged view showing a portion of the racket of FIG. 1 .

FIG. 3 is an exploded view showing a portion of the racket of FIG. 1 .

FIG. 4 is an enlarged perspective view showing a portion of a grommet of the racket of FIG. 3 .

FIG. 5A is an enlarged cross-sectional view of a portion of the grommet of FIG. 4 as viewed from the front.

FIG. 5B is a cross-sectional view taken along the line B-B of FIG. 5A.

FIG. 5C is a view for illustrating the shape of the tip opening of FIG. 5B.

FIG. 6A is an enlarged cross-sectional view of a portion of the grommet of FIG. 4 as viewed from the front.

FIG. 6B is a cross-sectional view taken along the line B-B of FIG. 6A.

FIG. 7 is an enlarged cross-sectional view of the vicinity of the top of the racket of FIG. 1 as viewed from the front.

FIG. 8 is a view of the vicinity of the top of the racket of FIG. 1 as viewed in an axial direction Y of the racket.

FIG. 9 is a front view showing the racket of FIG. 1 along with a ball.

FIG. 10A is an enlarged cross-sectional view of the vicinity of the top of the racket of FIG. 9 as viewed from the front.

FIG. 10B is a view for illustrating how a string moves upon contact of the ball with the face.

FIG. 11 is a view for illustrating a grommet according to Comparative Example 1.

FIG. 12 is a view for illustrating a grommet according to Comparative Example 2.

FIG. 13 is a view of a portion of a grommet of a racket according to a second embodiment of the present disclosure.

FIG. 14 is a view for illustrating how a string moves upon contact of a ball with the face of the racket of FIG. 13 .

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, the present disclosure will be described in detail based on preferred embodiments with appropriate reference to the drawings.

First Embodiment

FIGS. 1 to 3 show a tennis racket 2. The tennis racket 2 includes a frame 4, a grip 6, grommets 8, and strings 10. The tennis racket 2 is usable for regular tennis. In the drawings, the arrow X represents the width direction of the tennis racket 2, and the arrow Y represents the axial direction of the tennis racket 2. The reference sign CL represents the centerline of the tennis racket 2. The tennis racket 2 is symmetrical about the centerline CL.

The frame 4 includes a head 12, two throats 14, and a shaft 16. The head 12 defines the outline of the face 17 (described in detail later). The head 12 as viewed from the front is generally shaped as an ellipse. The direction of the major axis of the ellipse coincides with the axial direction Y of the tennis racket 2. The direction of the minor axis of the ellipse coincides with the width direction X of the tennis racket 2. One end of each throat 14 is continuous with the head 12. The throat 14 joins the other throat 14 in the vicinity of the other end. The throat 14 extends from the head 12 to the shaft 16. The shaft 16 extends from the point where the two throats 14 join each other. The shaft 16 is continuous and integral with the throats 14. The portion of the head 12 that is located between the two throats 14 is a yoke 18. The head 12 may have a shape other than an elliptical shape.

The frame 4 is formed of a pipe. That is, the frame 4 is hollow. The pipe is made of a fiber-reinforced resin material. The matrix resin of the fiber-reinforced resin material is a thermosetting resin. The thermosetting resin is typically an epoxy resin. The fibers of the fiber-reinforced resin material are typically carbon fibers. The fibers are continuous fibers.

The grip 6 is formed by a tape wound around the shaft 16. The grip 6 reduces slip between the hand(s) of the player and the tennis racket 2 when the player swings the tennis racket 2.

As shown in FIG. 3 , the tennis racket 2 includes a first grommet 8 a, two second grommets 8 b, and a third grommet 8 c. Each grommet 8 includes a base 20 and a plurality of tubular parts 100. Each tubular part 100 is integral with the base 20. The grommet 8 is typically made of a synthetic resin material softer than the material of the frame 4.

As shown by the arrow A1 in FIG. 3 , the first grommet 8 a is mounted around the top of the head 12. With the first grommet 8 a mounted on the head 12, each tubular part 100 of the first grommet 8 a extends through a corresponding one of holes (not shown) of the head 12. As shown by the arrow A2 in FIG. 3 , each second grommet 8 b is mounted on a corresponding one of the sides of the head 12. With the second grommet 8 b mounted on the head 12, each tubular part 100 of the second grommet 8 b extends through a corresponding one of holes (not shown) of the head 12. As shown by the arrow A3 in FIG. 3 , the third grommet 8 c is mounted on the yoke 18. With the third grommet 8 c mounted on the yoke 18, each tubular part 100 of the third grommet 8 c extends through a corresponding one of holes (not shown) of the head 12.

The strings 10 are strung on the head 12. The strings 10 are strung along the width direction X and the axial direction Y. The strings 10 that extend along the width direction X may be referred to as “transverse strings 10 a”. The strings 10 that extend along the axial direction Y may be referred to as “longitudinal strings 10 b”. The plurality of transverse strings 10 a and the plurality of longitudinal strings 10 b form the face 17 (see FIG. 1 ). The face 17 extends generally along the X-Y plane.

FIG. 4 is an enlarged perspective view showing a portion of the grommet 8 of the tennis racket 2 of FIG. 3 . The reference sign CP represents a plane passing through the centerline CL of the tennis racket 2 and perpendicular to the width direction X of the tennis racket 2 (this plane will be referred to as “reference plane” hereinafter). The tennis racket 2 is symmetrical about the reference plane CP. As previously stated, the grommet 8 includes the base 20 and the plurality of tubular parts 100.

The tubular part 100 has a through hole 24 (24 a or 24 b) through which the string 10 is passed. The plurality of tubular parts 100 include a plurality of tubular parts 100 a each of which has a through hole 24 a having a generally triangular cross-section and a plurality of tubular parts 100 b each of which has a through hole 24 b having an elliptical cross-section.

FIG. 5A is a cross-sectional view taken along a plane including the axis of the tubular part 100 a. FIG. 5B is a cross-sectional view taken along a plane perpendicular to the axis of the tubular part 100 a. The through hole 24 a includes a base opening 26 a, a side wall 28 a, and a tip opening 30 a. As previously stated, the through hole 24 a has a generally triangular cross-section. The cross-section of the through hole 24 a is congruent from the base opening 26 a to the tip opening 30 a. Thus, the tip opening 30 a is generally triangular.

In FIGS. 5A and 5B, the string 10 is shown by a dashed-double dotted line. In the tubular part 100 a having the tip opening 30 a, the string 10 is in contact with the side wall 28 a from the base opening 26 a to the tip opening 30 a which is generally triangular.

The shape of the tip opening 30 a will be described in more detail with reference to FIG. 5C. In FIG. 5C, the edges of the tip opening 30 a as viewed in the direction in which the through hole 24 a extends are shown by a bold solid line. The direction in which the through hole 24 a extends is parallel to the axial direction of the tubular part 100 a. The tip opening 30 a is symmetrical about a given plane R parallel to the face 17 (this plane R will be referred to as “face plane R” hereinafter). The tip opening 30 a is shaped as a triangle with rounded corners. The tip opening 30 a has three rounded vertices. The face plane R crosses one of the three vertices. Each of the vertices is formed by a curve but may be formed as a point.

In FIG. 5C, an imaginary dividing plane S dividing the tip opening 30 a into a first opening portion 31 and a second opening portion 32 in a direction parallel to the face 17 is shown by a dashed-double dotted line. The dividing plane S is perpendicular to the face 17. The dividing plane S is parallel to the direction in which the through hole 24 a extends. The length L1 of the first opening portion 31 in the direction parallel to the face 17 is greater than the length L2 of the second opening portion 32 in the direction parallel to the face 17.

One end of the tip opening 30 a in the direction parallel to the face 17 is referred to as a “first end P1”, which is an end of the first opening portion 31 as well. The other end of the tip opening 30 a in the direction parallel to the face 17 is referred to as a “second end P2”, which is an end of the second opening portion 32 as well. The length L1 of the first opening portion 31 is a distance between the first end P1 and the dividing plane S in the direction parallel to the face 17. The length L2 of the second opening portion 32 is a distance between the second end P2 and the dividing plane S in the direction parallel to the face 17.

The first opening portion 31 is generally shaped as a triangle having a vertex at the first end P1 of the tip opening 30 a in the direction parallel to the face 17. The inside dimension Lh of the first opening portion 31 in a direction perpendicular to the face 17 increases gradually from the first end P1 to the dividing plane S. In the present embodiment, as shown in FIG. 5C, the imaginary dividing plane S is at a location where the inside dimension Lh of the tip opening 30 a in the direction perpendicular to the face 17 reaches a maximum.

As shown in FIG. 5C, each of the two edges of the first opening portion 31 that extend from the first end P1 to the dividing plane S includes a straight portion 33 that is straight when viewed in the direction in which the through hole 24 a extends. The two straight portions 33 are symmetrical to each other about the face plane R. The ratio of the length L3 of the straight portion 33 in the direction parallel to the face 17 to the length L1 of the first opening portion 31 in the direction parallel to the face 17 (L3/L1) is 0.3 or more, preferably 0.5 or more, and more preferably 0.7 or more.

The angle θ between extensions of the two straight portions 33 is 120 degrees or less and preferably 90 degrees or less. The magnitude of the angle θ may differ from one tubular part 100 a to another. This will be described in detail later.

As shown by a dashed-double dotted line in FIGS. 5A and 5B, the string 10 is placed to pass through the first opening portion 31 (see FIG. 5C). More specifically, when viewed in the direction in which the through hole 24 a extends, the string 10 is in contact with that rounded vertex of the tip opening 30 a which includes the first end P1. As the cross-section of the through hole 24 a is congruent from the base opening 26 a to the tip opening 30 a, the string 10 can be in contact with the side wall 28 a from the base opening 26 a to the tip opening 30 a. As is clear from FIGS. 5A and 5B, the length L1 of the first opening portion 31 in the direction parallel to the face 17 is significantly greater than the diameter of the string 10. In the vicinity of the dividing plane S, the length of the first opening portion 31 in the direction perpendicular to the face 17 is significantly greater than the diameter of the string 10, while in the vicinity of the first end P1, the length of the first opening portion 31 in the direction perpendicular to the face 17 is not significantly greater than the diameter of the string 10. The tubular part 100 a permits the movement of the string 10 toward the dividing plane S.

FIG. 6A is a cross-sectional view taken along a plane including the axis of the tubular part 100 b. FIG. 6B is a cross-sectional view taken along a plane perpendicular to the axis of the tubular part 100 b. The through hole 24 b includes a base opening 26 b, a side wall 28 b, and a tip opening 30 b. As previously stated, the through hole 24 b has an elliptical cross-section. The cross-section of the through hole 24 b is congruent from the base opening 26 a to the tip opening 30 a. Thus, the tip opening 30 b is elliptical. The direction of the minor axis of the ellipse of the tip opening 30 b coincides with the direction parallel to the face 17 (the left-right direction in FIG. 6B).

In FIGS. 6A and 6B, the string 10 is shown by a dashed-double dotted line. The string 10 is placed to pass through the center of the ellipse of the tip opening 30 b. More specifically, the minor axis of the ellipse of the tip opening 30 b crosses the string 10 when viewed in the direction in which the through hole 24 b extends. For example, the string 10 may be in contact with the side wall 28 b in the direction parallel to the face 17 from the base opening 26 b to the tip opening 30 b. As is clear from FIGS. 6A and 6B, the inside dimension of the tip opening 30 b in the direction perpendicular to the face 17 is significantly greater than the diameter of the string 10. The tubular part 100 b permits the movement of the string 10 mainly in the direction perpendicular to the face 17.

As shown in FIG. 2 , the tennis racket 2 includes a first tubular part 101, a second tubular part 102, a third tubular part 103, a fourth tubular part 104, a fifth tubular part 105, a sixth tubular part 106, a seventh tubular part 107, an eighth tubular part 108, a ninth tubular part 109, a tenth tubular part 110, an eleventh tubular part 111, a twelfth tubular part 112, a thirteenth tubular part 113, a fourteenth tubular part 114, a fifteenth tubular part 115, a sixteenth tubular part 116, a seventeenth tubular part 117, an eighteenth tubular part 118, a nineteenth tubular part 119, a twelfth tubular part 120, a twenty-first tubular part 121, a twenty-second tubular part 122, a twenty-third tubular part 123, a twenty-fourth tubular part 124, a twenty-fifth tubular part 125, a twenty-sixth tubular part 126, a twenty-seventh tubular part 127, a twenty-eighth tubular part 128, a twenty-ninth tubular part 129, a thirtieth tubular part 130, a thirty-first tubular part 131, a thirty-second tubular part 132, a thirty-third tubular part 133, a thirty-fourth tubular part 134, and a thirty-fifth tubular part 135. In FIG. 2, 35 tubular parts 100 are shown. As previously stated, the tennis racket 2 is symmetrical about the centerline CL. Thus, the number of the tubular parts 100 in the tennis racket 2 is 70.

As shown in FIG. 2 , the longitudinal strings 10 b are passed through the first tubular part 101, second tubular part 102, third tubular part 103, fourth tubular part 104, fifth tubular part 105, sixth tubular part 106, seventh tubular part 107, ninth tubular part 109, twenty-seventh tubular part 127, twenty-ninth tubular part 129, thirtieth tubular part 130, thirty-first tubular part 131, thirty-second tubular part 132, thirty-third tubular part 133, thirty-fourth tubular part 134, and thirty-fifth tubular part 135. The transverse strings 10 a are passed through the eighth tubular part 108, tenth tubular part 110, eleventh tubular part 111, twelfth tubular part 112, thirteenth tubular part 113, fourteenth tubular part 114, fifteenth tubular part 115, sixteenth tubular part 116, seventeenth tubular part 117, eighteenth tubular part 118, nineteenth tubular part 119, twelfth tubular part 120, twenty-first tubular part 121, twenty-second tubular part 122, twenty-third tubular part 123, twenty-fourth tubular part 124, twenty-fifth tubular part 125, twenty-sixth tubular part 126, and twenty-eighth tubular part 128.

In the present embodiment, each of the second, fourth, and sixth tubular parts 102, 104, and 106 has the through hole 24 a having a generally triangular cross-section (see FIG. 5 ). Each of the other tubular parts 100 has the through hole 24 b having an elliptical cross-section (see FIG. 6 ). Any of the tubular parts 100 other than the second, fourth, and sixth tubular parts 102, 104, and 106 may have the through hole 24 a having a generally triangular cross-section or have a through hole having a circular cross-section.

FIG. 7 is an enlarged view of the vicinity of the top of the racket 2 of FIG. 1 as viewed from the front. FIG. 8 is a view of the vicinity of the top of the racket 2 of FIG. 1 as viewed in the axial direction Y. In FIGS. 7 and 8 , the frame 4 and the transverse strings 10 a are omitted. In FIG. 7 , there are shown the base 20, first tubular part 101, second tubular part 102, third tubular part 103, and fourth tubular part 104. In FIG. 8 , there are shown the base 20, first tubular part 101, second tubular part 102, third tubular part 103, fourth tubular part 104, fifth tubular part 105, and sixth tubular part 106. Each of the first, third, and fifth tubular parts 101, 103, and 105 has the through hole 24 b having an elliptical cross-section (see FIG. 6 ). Each of the second, fourth, and sixth tubular parts 102, 104, and 106 has the through hole 24 a having a generally triangular cross-section (see FIG. 5 ). In each of the second, fourth, and sixth tubular parts 102, 104, and 106, the string 10 is in contact with the left wall surface (inner one of the opposite wall surfaces in the width direction) of the side wall 28 a of the through hole 24 a.

As shown in FIG. 8 , the second, fourth, and sixth tubular parts 102, 104, and 106 are identical in that each of them has the generally triangular tip opening 30 a; however, the generally triangular shape slightly differs among the second, fourth, and sixth tubular parts 102, 104, and 106. Specifically, in the second tubular part 102, the angle θ1 between extensions of the two straight portions 33 included in the edges of the tip opening 30 a is 30 degrees. In the fourth tubular part 104, the angle θ2 between extensions of the two straight portions 33 included in the edges of the tip opening 30 a is 60 degrees. In the sixth tubular part 106, the angle θ3 between extensions of the two straight portions 33 included in the edges of the tip opening 30 a is 90 degrees. That is, the closer the tubular part is to the centerline CL of the racket 2, the smaller is the angle θ between extensions of the two straight portions (θ1<θ2<θ3). The angle θ between extensions of the two straight portions 33 included in the edges of the tip opening 30 a may be the same for the second, fourth, and sixth tubular parts 102, 104, and 106.

In the tip opening 30 a of each of the second, fourth, and sixth tubular parts 102, 104, and 106, the first opening portion 31 is closer to the centerline CL of the racket 2 than the second opening portion 32.

FIG. 9 shows the tennis racket 2 along with a tennis ball B. FIG. 9 illustrates the moment of impact between the tennis racket 2 and the tennis ball B. In FIG. 9 , the tennis ball B collides with the face 17 at a point below the centerline CL (point toward the ground G). In this state, the player swings the tennis racket 2 forward and upward.

As a result of the swing, the longitudinal string 10 b passed through the second tubular part 102 is subjected to a force acting perpendicular to the face 17 and outward in the width direction. In FIG. 10A, the longitudinal string 10 b moved by the force is shown. In FIG. 10B, the direction in which the ball B contacts the face 17 is shown by the arrow B1, and the direction in which the longitudinal string 10 b moves upon contact of the ball B with the face 17 is shown by the arrow depicted inside the through hole 24 a. The longitudinal string 10 b is deformed without being disturbed by the second tubular part 102 and moves outward in the width direction. In the tip opening 30 a, the longitudinal string 10 b is pushed by the ball B and moves toward the dividing plane S along the edge of the first opening portion 31 that is opposite from the ball B. After that, the longitudinal string 10 b is restored to its original shape. Likewise, the longitudinal strings 10 b passed through the fourth tubular part 104 (100 a) and sixth tubular part 106 (100 a) are deformed and then restored to their original shapes. The deformation and restoration of the longitudinal strings 10 b ensure a long time of contact between the tennis racket 2 and the tennis ball B. With the use of the tennis racket 2, the tennis ball B is shot at a large launch angle. With the use of the tennis racket 2, a high trajectory of the tennis ball B can be achieved even in the event that the tennis ball B is hit at a point below the centerline CL.

As previously stated, the string 10 is in contact with the inner one of the opposite wall surfaces of the side wall 28 a of the through hole 24 a in the width direction. Thus, when the tennis ball B collides with the face 17 at a point above the centerline CL, the deformation of the longitudinal string 10 b is not facilitated by the generally triangular through hole 24 a. As such, a long time of contact is not achieved, and correction of the trajectory does not occur. With the use of the racket 2, there is little difference in trajectory between collision of the tennis ball B with the face 17 at a point above the centerline CL and collision of the tennis ball B with the face 17 at a point below the centerline CL.

As previously stated, the string 10 is pushed by the ball B and moves toward the dividing plane S along the edge of the first opening portion 31 that is opposite from the ball B. As the movement direction of the string 10 is restricted in this manner, a stable trajectory can be achieved with reduced variations in both the launch angle and flight distance. As the tip opening 30 a is symmetrical about a plane parallel to the face 17, a stable trajectory can be achieved regardless of which side of the face 17 the ball B collides with.

In the first tubular part 101, the tip opening 30 b is shaped as an ellipse having a minor axis the direction of which coincides with the direction parallel to the face 17. Thus, the longitudinal string 10 b passed through the first tubular part 101 is deformed in the direction perpendicular to the face 17 under the action of the pressing force applied from the tennis ball B. The first tubular part 101 does not hinder this deformation. However, the first tubular part 101 hinders the deformation of the string 10 in the direction parallel to the face 17. Thus, the string 10 passed through the through hole 24 b of the first tubular part 101 and the string 10 passed through the through hole 24 a of the second tubular part 102 adjacent to the first tubular part 101 move away from each other under the action of the pressing force applied from the tennis ball B. Thus, the distance between the two strings 10 is increased upon contact of the ball B with the face 17, and this makes it easier to spin the ball B.

Likewise, the distance between the string 10 passed through the through hole 24 b of the third tubular part 103 and the string 10 passed through the through hole 24 a of the fourth tubular part 104 is increased under the action of the pressing force applied from the tennis ball B. The distance between the string 10 passed through the through hole 24 b of the fifth tubular part 105 and the string 10 passed through the through hole 24 a of the sixth tubular part 106 is also increased under the action of the pressing force applied from the tennis ball B.

The edges of the first opening portion 31 of each of the second, fourth, and sixth tubular parts 102, 104, and 106 include the two straight portions 33 which are symmetrical to each other about a plane parallel to the face 17. Extensions of the two straight portions 33 in each of the second, fourth, and sixth tubular parts 102, 104, and 106 form an angle θ with each other, and the closer the tubular part is to the centerline CL of the racket 2, the smaller the angle θ between the extensions is (that is, θ1<θ2<θ3). This allows the string 10 to move in an appropriate direction in each tubular part. In general, the flight distance of the ball decreases as the ball hitting point becomes more distant from the center of the face of the racket. However, in the present embodiment, the angle θ between extensions of the two straight portions 33 increases with increasing distance from the tubular part to the centerline CL of the racket 2, so that the farther the tubular part is from the centerline CL, the more easily the string 10 can move in a direction perpendicular to a ball hitting plane. Thus, a desired flight distance is likely to be achieved even in the event that the ball is hit at a point away from the centerline CL of the racket 2.

In order to endow the tennis racket 2 with performance intended by the designer, the tubular part 100 a may be formed such that the string 10 is in contact with the outer one of the opposite wall surfaces in the width direction.

In the tennis racket 2, each of the tubular parts 100 a located in the vicinity of the top of the tennis racket 2 (second, fourth, sixth tubular parts 102, 104, and 106) has the through hole 24 a having a generally triangular cross-section. Any of the tubular parts 100 located on the yoke 18 may have the through hole 24 a having a generally triangular cross-section. Any of the tubular parts 100 located on the sides of the head 12 may have the through hole 24 a having a generally triangular cross-section. Any of the transverse strings 10 a may be passed through the tubular part 100 having the through hole 24 a having a generally triangular cross-section. In any case, the height of trajectory exhibited upon collision of the tennis ball B with a given area of the face 17 can be increased.

In the tennis racket 2, as previously stated, each of the second, fourth, and sixth tubular parts 102, 104, and 106 has the through hole 24 a having a generally triangular cross-section. Being symmetrical about the centerline CL, the tennis racket 2 includes two second tubular parts 102, two fourth tubular parts 104, and two sixth tubular parts 106. Thus, the total number N of the tubular parts 100 a having the through hole 24 a, which has a generally triangular cross-section and in which the string 10 b is in contact with the inner one of the opposite wall surfaces in the width direction, is six. The total number N need not be 6. For example, the total number N is preferably from 2 to 16 and more preferably from 4 to 12.

Evaluation Test

An evaluation test was conducted in which the effect of the racket 2 including the tubular part 100 a having the through hole 24 a having a generally triangular cross-section was evaluated by comparing the racket 2 with other rackets. In the evaluation test, three types of rackets, i.e., rackets of Example, Comparative Example 1, and Comparative Example 2 were produced first.

A racket including second, fourth, and sixth tubular parts was produced as the racket of Example. Each of the second, fourth, and sixth tubular parts had a through hole 24 a having a generally triangular cross-section, like the second, fourth, and sixth tubular parts 102, 104, and 106 described in the above embodiment.

FIG. 11 shows a second tubular part 200 of the racket of Comparative Example 1. The through hole 201 of the second tubular part 200 has a circular cross-section. The cross-section of the through hole 201 is congruent from the base opening to the tip opening. The diameter of the through hole 201 is only slightly greater than the diameter of the string 10, and the string 10 is hardly movable in the through hole 201. In Comparative Example 1, the cross-sections of the through holes of the fourth and sixth tubular parts have the same shape as the cross-section of the through hole 201 of the second tubular part 200.

FIG. 12 shows a second tubular part 300 of the racket of Comparative Example 2. The through hole 301 of the second tubular part 300 has a circular cross-section. The cross-section of the through hole 301 is congruent from the base opening to the tip opening. The diameter of the through hole 301 is significantly greater than the diameter of the string 10. The diameter of the through hole 301 is two or more times the diameter of the string 10. In the tubular part 300, the string 10 is in contact with the inner one of the opposite wall surfaces of the side wall of the through hole 301 in the width direction. The tubular part 300 restricts the string 10 from moving inward along the width direction in the through hole 301, and does not restrict the movement of the string 10 in other directions. In Comparative Example 2, the cross-sections of the through holes of the fourth and sixth tubular parts have the same shape as the cross-section of the through hole 301 of the second tubular part 300.

In each of the rackets of Example, Comparative Example 1, and Comparative Example 2, the through holes of tubular parts other than the second, fourth, and sixth tubular parts had the same circular cross-section. Specifically, the shape of the through holes of tubular parts other than the second, fourth, and sixth tubular parts was the same as the shape of the through hole 201 shown in FIG. 11 .

After production of the three types of rackets of Example, Comparative Example 1, and Comparative Example 2 as described above, players were allowed to play rallies using the different types of rackets. The ball trajectories were tracked for each racket, and the average and standard deviation of the launch angle of the ball were calculated. The average and standard deviation of the flight distance of the ball were also calculated. The calculation results are listed in Table 1.

TABLE 1 Comparative Comparative Example Example 1 Example 2 Launch Average (°) 10.5 9.9 9.6 angle Standard deviation 0.64 1.31 1.50 Flight Average (m) 24.4 23.9 23.9 distance Standard deviation 0.90 1.58 1.99

As seen from Table 1, the average of the launch angle was greater in Example 1 than in Comparative Examples 1 and 2. The average of the flight distance was also greater in Example than in Comparative Examples 1 and 2. This verifies that the racket of Example is superior to the rackets of Comparative Examples 1 and 2 in both the launch angle and flight distance.

Additionally, the standard deviation from the average of the launch angle was smaller in Example than in Comparative Examples 1 and 2, and the standard deviation from the average of the flight distance was also smaller in Example than in Comparative Examples 1 and 2. This verifies that the racket of Example produces a more stable trajectory with smaller variations in both the launch angle and flight distance than the rackets of Comparative Examples 1 and 2.

Second Embodiment

FIG. 13 shows a portion of a grommet 40 of a tennis racket according to a second embodiment. This tennis racket has the same structural components as the tennis racket 2 shown in FIGS. 1 to 12 , except for the grommet 40. In the following description, the structural components of the grommet 40 that are the same as those of the grommet of the first embodiment are denoted by the same reference signs and will not be described in detail.

The grommet 40 includes a base 20 and tubular parts 100. Each tubular part 100 has a through hole 24 thorough which a string 10 is passed. The cross-section of the through hole 24 is congruent from the base opening to the tip opening. The plurality of tubular parts 100 include tubular parts 100 a and 100 c each of which has a through hole 24 a or 24 c having a cross-section shaped as described in the first embodiment. Each of the through holes 24 a and 24 c has a generally triangular cross-section just as does the through hole 24 a described in the first embodiment. The orientation of the generally triangular shape differs between the through holes 24 a and the through holes 24 c.

Specifically, as shown in FIG. 13 , the through hole 24 c of the tubular part 100 c has a cross-section that is symmetrical to that of the through hole 24 a of the tubular part 100 a about a line perpendicular to the face 17. The cross-section of the through hole 24 a and the cross-section of the through hole 24 c are in different orientations but are congruent to each other. The tubular parts 100 a and the tubular parts 100 c alternate with one another.

The angle between extensions of the two straight portions included in the edges of the tip opening is the same for all of the tubular parts 100 a and 100 c shown in FIG. 13 . However, the angle between extensions of the two straight portions included in the edges of the tip opening may differ for each tubular part 100 a or 100 c. The magnitude of the angle between extensions of the two straight portions may be chosen as appropriate.

The present embodiment differs from the first embodiment also in that in the tubular parts 100 a and 100 c, the first opening portion 31 need not be closer to the centerline CL of the racket 2 than the second opening portion 32. For example, when the first opening portion 31 is closer to the centerline CL of the racket 2 than the second opening portion 32 in one of the two tubular parts 100 a and 100 c adjacent to each other, the first opening portion 31 may be farther from the centerline CL of the racket 2 than the second opening portion 32 in the other of the adjacent tubular parts 100 a and 100 c.

The grommet 40 is mounted around the top of the head 12. The grommet 40 may be mounted on one of the sides of the head 12 or on the yoke 18.

FIG. 14 is a view for illustrating how the string 10 moves upon contact of a ball with the face of the racket of FIG. 13 . FIG. 14 shows one tubular part 100 a and one tubular part 100 c which are adjacent to each other.

The present embodiment, like the first embodiment, has the advantage of increasing both the launch angle and flight distance. Additionally, the present embodiment, like the first embodiment, has the advantage of producing a stable trajectory with reduced variations in both the launch angle and flight distance.

Furthermore, in the present embodiment, the string 10 passed through the through hole 24 a of the tubular part 100 a and the string 10 passed through the through hole 24 a of the tubular part 100 c adjacent to the tubular part 100 a move away from each other. Thus, the maximum value of the distance between the two adjacent strings 10 is increased upon contact of the ball with the face. This makes it easier to spin the ball.

Other Embodiments

Although in the above embodiments the imaginary dividing plane S is at a location where the inside dimension of the tip opening 30 a in the direction perpendicular to the face 17 reaches a maximum, the imaginary dividing plane S is not limited to being at this location. The dividing plane may be defined at any location, provided that the first opening portion is longer than the second opening portion in the direction parallel to the face and that the inside dimension of the first opening portion in the direction perpendicular to the face increases gradually from one end of the first opening portion in the direction parallel to the face to the dividing plane.

Although in the above embodiments the cross-section of the through hole is congruent from the base opening to the tip opening, the cross-section of the through hole need not be congruent from the base opening to the tip opening. For example, the through hole may have a generally triangular tip opening as described in the above embodiments and a base opening having a shape other than a generally triangular shape, such as a circular base opening. For example, the through hole may have a generally triangular tip opening as described in the above embodiments, and the cross-section of the through hole may change continuously or stepwise toward the base opening.

Although in the above first embodiment the direction of the minor axis of the ellipse of the tip opening 30 b coincides with the direction parallel to the face 17 (the left-right direction in FIG. 6B), the minor axis of the ellipse of the tip opening 30 b may cross the direction parallel to the face 17 (the left-right direction in FIG. 6B). The tip opening 30 b may be circular. In this case, the tip opening 30 b may be, for example, an opening as shown in FIG. 11 which permits little movement of the string or an opening as shown in FIG. 12 which permits movement of the string.

The tip opening including the first and second opening portions need not be generally triangular. The tip opening may be generally shaped as a rectangle composed of a generally triangular first opening portion and a generally triangular second opening portion that is shorter than the generally triangular first opening portion in the direction parallel to the face. The tip opening may be fan-shaped. The tip opening may be asymmetrical about a plane parallel to the face.

[Disclosed Items]

The following items disclose preferred embodiments.

[Item 1]

A racket including: a frame; a grommet mounted on the frame, the grommet including a plurality of tubular parts; and strings forming a face of the racket, wherein: each of the tubular parts includes a through hole through which a corresponding one of the strings is passed; the through hole includes a base opening, a side wall, and a tip opening; at least one of the plurality of tubular parts includes a non-circular tip opening; assuming an imaginary dividing plane that is perpendicular to the face and that divides the non-circular tip opening into a first opening portion and a second opening portion shorter than the first opening portion in a direction parallel to the face, an inside dimension of the first opening portion in a direction perpendicular to the face increases gradually from one end of the non-circular tip opening in the direction parallel to the face to the dividing plane; and in the tubular part including the non-circular tip opening, the string passes through the first opening portion and is in contact with the side wall from the base opening to the tip opening.

[Item 2]

The racket according to item 1, wherein the first opening portion is generally shaped as a triangle having a vertex at the one end of the non-circular tip opening.

[Item 3]

The racket according to item 1 or 2, wherein the first opening portion is closer to a centerline of the racket than the second opening portion.

[Item 4]

The racket according to any one of items 1 to 3, wherein the first opening portion includes an edge extending from the one end to the dividing plane, the edge including a straight portion that is straight when viewed in a direction in which the through hole extends, and a ratio of a length of the straight portion in the direction parallel to the face to a length of the first opening portion in the direction parallel to the face is 0.3 or more.

[Item 5]

The racket according to any one of items 1 to 4, wherein the string passed through the tubular part including the non-circular tip opening is a longitudinal string.

[Item 6]

The racket according to item 5, wherein the tubular part including the non-circular tip opening is located in the vicinity of a top of the frame.

[Item 7]

The racket according to any one of items 1 to 6, wherein: the plurality of tubular parts include two or more tubular parts each of which includes the non-circular tip opening, the two or more tubular parts being located in the vicinity of a top of the frame; edges of the first opening portion of each of the two or more tubular parts include two straight portions each of which is straight when viewed in a direction in which the through hole extends, the two straight portions being symmetrical to each other about a plane parallel to the face; extensions of the two straight portions in each of the two or more tubular parts form an angle with each other; and the closer the tubular part is to a centerline of the racket, the smaller the angle between the extensions is.

The racket according to the present disclosure can be used in various kinds of sports such as soft tennis, squash, and badminton.

From the foregoing description, numerous modifications and other embodiments of the present disclosure are obvious to those skilled in the art. Accordingly, the foregoing description is to be construed as illustrative only, and is provided for the purpose of teaching those skilled in the art the best mode for carrying out the present disclosure. The structural and/or functional details may be substantially modified without departing from the scope of the present disclosure. 

What is claimed is:
 1. A racket comprising: a frame; a grommet mounted on the frame, the grommet including a plurality of tubular parts; and strings forming a face of the racket, wherein each of the tubular parts includes a through hole through which a corresponding one of the strings is passed, the through hole includes a base opening, a side wall, and a tip opening, at least one of the plurality of tubular parts includes a non-circular tip opening, assuming an imaginary dividing plane that is perpendicular to the face and that divides the non-circular tip opening into a first opening portion and a second opening portion shorter than the first opening portion in a direction parallel to the face, an inside dimension of the first opening portion in a direction perpendicular to the face increases gradually from one end of the non-circular tip opening in the direction parallel to the face to the dividing plane, and in the tubular part including the non-circular tip opening, the string passes through the first opening portion and is in contact with the side wall from the base opening to the tip opening.
 2. The racket according to claim 1, wherein the first opening portion is generally shaped as a triangle having a vertex at the one end of the non-circular tip opening.
 3. The racket according to claim 1, wherein the first opening portion is closer to a centerline of the racket than the second opening portion.
 4. The racket according to claim 1, wherein the first opening portion includes an edge extending from the one end to the dividing plane, the edge including a straight portion that is straight when viewed in a direction in which the through hole extends, and a ratio of a length of the straight portion in the direction parallel to the face to a length of the first opening portion in the direction parallel to the face is 0.3 or more.
 5. The racket according to claim 1, wherein the string passed through the tubular part including the non-circular tip opening is a longitudinal string.
 6. The racket according to claim 5, wherein the tubular part including the non-circular tip opening is located in the vicinity of a top of the frame.
 7. The racket according to claim 1, wherein the plurality of tubular parts include two or more tubular parts each of which includes the non-circular tip opening, the two or more tubular parts being located in the vicinity of a top of the frame, edges of the first opening portion of each of the two or more tubular parts include two straight portions each of which is straight when viewed in a direction in which the through hole extends, the two straight portions being symmetrical to each other about a plane parallel to the face, extensions of the two straight portions in each of the two or more tubular parts form an angle with each other, and the closer the tubular part is to a centerline of the racket, the smaller the angle between the extensions is. 